The present invention relates generally to the field of semiconductor processing equipment. More particularly, the present invention relates to a method and apparatus for dispensing fluids onto a semiconductor substrate. Merely by way of example, the method and apparatus has been applied to two processing chambers in a coat/develop module sharing a central fluid dispense bank. But it would be recognized that the invention has a much broader range of applicability.
Portions of the process of forming electronic devices are commonly performed in a multi-chamber processing system (e.g., a cluster tool) that has the capability to sequentially process substrates, (e.g., semiconductor wafers) in a controlled processing environment. A typical cluster tool used to deposit (i.e., coat) and develop a photoresist material, commonly known as a track lithography tool, will include a mainframe that houses multiple substrate transfer robots which transport substrates between a pod/cassette mounting device and multiple processing chambers that are connected to the mainframe. Cluster tools are often used so that substrates can be processed in a repeatable way in a controlled processing environment. A controlled processing environment has many benefits which include minimizing contamination of the substrate surfaces during transfer and during completion of the various substrate processing steps. Processing in a controlled environment thus reduces the number of generated defects and improves device yield.
Two types of processing chamber generally included in a track lithography tool are substrate coating modules and substrate developing modules, sometimes collectively referred to as a coat/develop module. Typically, in a coat module, a spin coating process is used to form a layer of photoresist or other coating on an upper surface of a substrate. One method mounts a substrate on a spin chuck, which is rotated at up to several thousand revolutions per minute (RPMs). Several milliliters of a liquid (e.g., photoresist) is applied to a central region of the substrate and the spinning action of the spin chuck disperses the liquid over the surface of the substrate. The coating is processed in subsequent steps to form features on the substrate as is well known to one of skill in the art. In develop modules, a developer is applied to the surface of the substrate after exposure of the photoresist. The coat/develop modules contain a number of similarities, as well as differences, including different nozzle designs corresponding to varying viscosities of dispense fluids, among other factors.
In some previously known coat/develop modules, a single spin bowl is attached to a system for dispensing photoresist or other coating liquids. In some photoresist coating applications, it is desirable to provide a number of different coatings, including different thicknesses and materials. Particularly, the industry transition to 300 mm substrates has led to an increase in the number of different coating liquids. Accordingly, in some coat/develop modules, and particularly in photoresist coat modules, the dispense system may include a number of different dispense nozzles dispensing different photoresists. Additionally, a number of other dispense nozzles may be included that provide photoresists with varying concentrations of solutions and solvents.
In some coat/develop modules, the dispense nozzles are fabricated to precise tolerances in accordance with the tolerances associated with a particular semiconductor process. As a result of the number and quality of the dispense nozzles in some of these modules, the cost of the dispense system may be much larger than the cost of the spin bowl.
In general, coat/develop applications rotate the substrate to achieve a predetermined rotation speed, dispense the coating fluid, and then continue rotating the substrate for a predetermined period after the dispense step is completed. As described above, the rotation of the substrate is utilized to disperse the coating fluid over the surface of the substrate. In these processes, the dispense system is inactive while the substrate rotation dispenses the resist. Therefore, in some dispense systems, the most expensive system components, namely those included in the dispense apparatus, are idle during a significant fraction of the processing time.
Other previously known coat modules employ multiple spin bowls. One example of a coating apparatus with two spin chucks located in a single casing is described in U.S. Pat. No. 5,250,114. Wafers are loaded and unloaded from the spin chucks by a single robot located outside the casing. A single resist nozzle for dispensing a resist liquid is attached to a nozzle arm attached to an endless belt surrounding two rollers. The endless belt is driven by a motor. Through use of the motor and endless belt, the nozzle arm is able to serve both spin chucks.
The system as illustrated in U.S. Pat. No. 5,205,114 suffers from several problems. First, the system provides only a single resist nozzle that dispenses a single resist. Thus, the system does not provide a number of different coatings, including coatings of different materials. Second, the only isolation provided between the spin chucks and the other items contained inside the casing is a cup surrounding each spin chuck. The cup is raised into position during coating. Although this cup design may provide some containment for liquid particles scattered from the wafer surface, control of the atmosphere in the vicinity of the wafers is not provided by this design. As a result, air-borne particles and solvent mist are free to move from one spin chuck to the other or from a waiting trench where the single nozzle waits to either of the wafers.
Therefore, a need exists in the art for improved coat/develop modules and improved methods of operating the same.